If you’re a nerd of a certain age (as I surely am), there’s a good chance you have a special place in your heart for the trials and tribulations of an earthling named Arthur Dent, his optimistic friend Trillian, and their adventures exploring the galaxy in the company an eccentric travel writer for The Hitchhiker’s Guide to the Galaxy. Oddities abound: The bureaucratic Vogons. Marvin the paranoid android. The babel fish. But, above all the absurdity and puns, there’s a clear reassurance: don’t panic!

I’m here to deliver the same message to anyone struggling to navigate the universe of mailbox providers. There’s a good reason why webmail and internet service providers (ISPs) require email senders to follow various rules and protocols if they want to reach the inbox: to help ensure their customers have a great experience, free of spam. But the complexity of the inbox universe can be challenging if you’re new to the email space, whether you’re a developer building email into your app or business process or a growth marketer using email to nurture customer engagement with your service. You’re not alone if you’ve wished for something like a babel fish to make sense of the idiosyncrasies of the email industry.

But like I said, don’t panic! Even though mailbox providers—from smaller ISPs to the biggest like Gmail—keep some proprietary details close to their vest, email sending best practices aren’t as mysterious as it might first appear.

Here are the basics any intrepid email explorer needs to navigate the galaxy of mailbox providers:

The universe of email inboxes is dominated by a few big mailbox providers, especially for consumers. For a decade or more, it’s been “The Big 4”: Gmail, Outlook/Hotmail, Yahoo!, and AOL, with a handful of ISPs like Comcast rounding out the landscape. (As more businesses move their apps to the cloud, business inboxes are beginning to behave more like consumer inboxes.)

It’s true that the path to the inbox has gotten more complicated, thanks to bad actors like spammers. But if you understand what happens after you hit send, it’s easier to solve deliverability problems when they do arise.

ISPs and mailbox providers really do want you to understandwhat you need to do to be successful. Listening to your customers’ signals—with the help of a babel fish, if necessary—is where it all begins.